Wireless Transceiver

ABSTRACT

In a MIMO wireless transceiver, priority control that judges priority of transmit data and a transmission mode table are provided to control an option as to which transmission system SDM or STBC is selected, coding rate and modulation method based on a transmission mode for a transmission destination that is determined by priority of transmission data and status of a communication matrix at the time of data transmission. With such arrangement, a wireless communication system composed of the MIMO wireless transceiver can control coding, MIMO signal processing and modulation methods according to priority of transmit data. More specifically, it is possible to ensure transmission of data having higher priority and improve throughput in total when a plurality of types of data are transmitted.

CLAIM OF PRIORITY

The present application is a continuation of application Ser. No.11/211,690 filed Aug. 26, 2005 which claims priority from Japaneseapplication JP 2005-156687, filed on May 30, 2005, the content of whichis hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a wireless transceiver of a MIMOwireless communication system which uses at least two or more antennasfor each of a transmitter and a receiver, and more specifically to awireless transceiver that is suitable for usage environment wheretransmission of image data, audio data, etc. is conducted and thustransmission quality is questioned.

BACKGROUND OF THE INVENTION

As a conventional wireless communication system, there is a wireless LANsystem that is standardized by the IEEE 802.11 (See non-patentreferences 1 and 2).

A technology in which transmission is controlled according to priorityof data has been known in the field of the wireless LAN technology.Patent reference 1 discloses a technology in which a coding rate and amodulation method are controlled according to priority of packets. Inaddition, patent reference 2 discloses a technology in which image datais transferred in the above-stated method. The standard of the TGe (IEEE802.11 Task Group e) for specific priority is described in non-patentreference 3 shown below, for example.

On the other hand, in the wireless LAN technology, a MIMO(Multiple-Input Multiple-Output) transmission system is attracting a lotof attention. The feature of the MIMO transmission lies in thearrangement that enables, in a wireless transceiver, higher transmissionspeed than that of conventional wireless LAN systems and stablecommunication even under multi-path (reflected wave) environment byperforming data transmission and reception by using a plurality ofantennas for subsequent data synthesis and decoding.

Known examples of the MIMO transmission include a method as shown innon-patent reference 4 in which original transmit data is divided into aplurality of transmission streams, which are then transmittedsimultaneously from a plurality of antennas (SDM: Space DivisionMultiplexing), and a method as shown in non-patent reference 5 in which,while using the same data rate as the case where an antenna is used foreach of regular transmission and reception, wireless transmission isperformed more securely than conventional methods by usingtransmission/reception diversity (STBC: Space Time Block Coding). TheMIMO signal processing under the SDM method makes it possible to set thedata rate higher in proportion to the number of transmission antennasunlike a wireless system where an antenna is used for each of regulartransmission and reception. While it will not make the data rate higher,the signal processing under the STBC method realizes more assuredwireless transmission with the increased number of antennas.

It should be noted that patent reference 3 shown below discloses awireless communication system of a hybrid type where a transmissionmethod according to the MIMO standard and a transmission method based onanother standard are combined.

[Patent Reference 1]

Japanese Patent Laid-open No. 2004-179821

[Patent Reference 2]

Japanese Patent Laid-open No. 2003-134077

[Patent Reference 3]

Japanese Patent Laid-open No. 2004-515176

[Non-patent Reference 1]

IEEE Std. 802.11a-1999, IEEE

[Non-patent Reference 2]

IEEE Std. 802.11g-2003, IEEE

[Non-patent Reference 3]

Edited by Masahiro Morikura, Shuji Kubota, “Revised 802.11 High-SpeedWireless LAN Text Book”, Dec. 21, 2004, Impress

[Non-patent Reference 4]

P. W. Wolniansky, G. J. Foschini, G. D. Golden, R. A. Valenzuela,“V-BLAST: An Architecture for Realizing Very High Data Rates Over theRich-Scattering Wireless Channel”, Proc. IEEE ISSSE-98, Pisa, Italy,Sep. 30, 1998, IEEE

[Non-patent Reference 5]

Vahid Torokh, Siavash M. Alamouti, Patric Poon, “New Detection Schemesfor Transmit Diversity with no Channel Estimation”, Proc. IEEEICUPC1998, pp. 917-920, Vol. 2

SUMMARY OF THE INVENTION

First, in order to describe problems, a configuration of a wirelesstransceiver of a wireless LAN system according to a prior art will bedescribed with reference to FIGS. 2 and 3.

FIG. 2 is a block diagram of a wireless transceiver of a wireless LANsystem according to the prior art. FIG. 3 is a diagram illustrating thattransmit data is stored in a queue of priority control unit in thepriority control of transmit data.

A wireless LAN system 1 according to the prior art is configured withwireless transceivers 2 a and 2 b. Transmit data 3 a is buffered in apriority control unit 10 a and is controlled so that data having higherpriority may be likely to be transmitted ahead of others. The transmitdata buffered in the priority control unit 10 a is then coded by anencoder 11 a to enhance error resistance characteristics during wirelesstransmission. Subsequently, the encoded transmit data is divided intotransmission streams by a MIMO signal processing unit 12 a. When anantenna 18 a is composed of two sub-antennas as shown in FIG. 2, theMIMO signal processing unit 12 a generates two transmission streams fromthe transmit data. The generating processes will be described later.

Here, operations of a priority control unit 10 will be described withreference to FIG. 3. The priority control unit 10 uses a system that isunder standardization by the IEEE 802.11 Task Group e (TGe) stated inthe above-stated patent reference 3 will be used. The transmit data 3 ais provided with priority in advance and is input to the prioritycontrol unit 10 by an application. In the priority control unit 10, thetransmit data is classified into four priority levels (101). Data wheregreat importance is given to latency like voice is provided with thehighest priority, and such data is classified here as AC_VO (102).Further, data where a slight amount of buffering is permitted like avideo signal is classified as AC_VD which has the second priority (103).Furthermore, regular data is classified as AC_BE which has the thirdpriority (104). Data having low urgency like background data isclassified as AC_BG which has the lowest priority (105). As shown inFIG. 3, buffers 102 to 105 are provided to store data therein accordingto the four classification categories. Each buffer is configured as aFIFO (First-In First-Out) structure allowing data to be output startingfrom the one that is input earlier. When data exists in either one ofsuch buffers, by arranging, as a step to determine the data to beactually transmitted, that data having higher priority is likely to betransmitted in terms of probability, it is possible to transmit datahaving higher priority on a priority basis.

Examples of the MIMO transmission system include two methods: one is theSDM shown in non-patent reference 4 which increases the data rate; andthe other is the STBC which is shown in non-patent reference 5.

The MIMO signal processing unit 12 a uses either of the above-stated SDMor STBC to generate two transmission streams. Each of the streams ismodulated by using an appropriate modulation method in a modulator 13 a,up-converted to a radio-frequency signal in a transmission RF (RadioFrequency) unit 14 a, and is transmitted from the antenna 18 a via atransmission/reception selector switch 17 a. In the receiver, the signalreceived at an antenna 18 b is amplified in a reception RF unit 20 b,down-converted therein, and is input to a demodulator 21 b. In order forthe receiver to obtain information such as the modulation method and thecoding rate that are used by the transmitter, a mechanism is requiredwhich notifies of the receiver the modulation method and the coding ratethat were used together with transmit data. Usually, such information istransmitted as header information of transmit data when the date istransmitted. Details of such frame structures can be realized by usingmethods that are disclosed in the above-stated non-patent references 1and 2. A plurality of signals that are decoded in the demodulator 21 bare input to a MIMO signal processing unit 22 b, converted into one datamatrix, and is then input to a decoder 23 b. The data of which errorsare corrected in the decoder 23 b is checked in a retransmission controlunit 24 b whether or not a reception frame is correctly received. If theretransmission control unit 24 b judges the reception frame is correctlyreceived, the control unit 24 b transmits an ACK (Acknowledgment) framewithin a specific time period. If the control unit 24 b judges thereception frame is wrongly received, the control unit 24 b transmits aNACK (Not Acknowledgment) frame within a specific time period or inpredetermined timing. Here, the ACK frames and the NACK frames shall bereferred to collectively as the responding frames. These respondingframes are configured in the retransmission control unit 24 b, input tothe encoder 11 b, and are processed as is the case with the transmissionprocessing of the transceiver 2 a described earlier before beingtransmitted. The transceiver 2 a is able to learn whether or not thetransmit data has been correctly received by receiving the respondingframe transmitted from the transceiver 2 b. Upon receipt of an ACKframe, the transceiver 2 a judges the transmit data could be correctlytransmitted to the transceiver 2 b, and erases the transmit data thathas been buffered in the priority control unit 10 a. Further, uponreceiving a NACK frame, or upon not receiving a responding frame withina prescribed time period or in prescribed timing, the transceiver 2 ajudges the transmit data could not be transmitted correctly to thetransceiver 2 b, and retransmits (resends) the data that was transmittedbefore. By repeating resending of the data, it is possible to finallytransmit the transmit data to the transmission destination. Here,occurrence of resending induces an assumption that conditions oftransmission matrix was likely to be poor at the time of transmittingthe earlier transmit data. Consequently, when resending the data, thetransceiver 2 a changes the modulation method, the coding rate and theMIMO signal processing method so that a method can be selected thatenables more secure data transmission than previous transmission.

For example, in the MIMO, the following table 1 shows combination of bitrates, modulation method and coding rate at the time of datatransmission.

TABLE 1 Bit Rate Modulation Coding Rate  6 Mbps BPSK ½  9 Mbps BPSK ¾ 12Mbps QPSK ½ 18 Mbps QPSK ¾ 24 Mbps 16 QAM ½ 36 Mbps 16 QAM ¾ 48 Mbps 64QAM ½ 54 Mbps 64 QAM ¾

An example shown in this table provides four types of modulation methodsBPSK, QPSK, 16 QAM and 64 QAM, and two types of coding rate ½ and ¾, andthus realizes 8 kinds of combination in total by combining themodulation methods with the coding rates with respective of one another.To achieve the maximum data rate, the 64 QAM can be chosen for themodulation method and the ¾ can be chosen for the coding rate. However,in this case, the error resistance characteristic becomes lower comparedto other types of combination. Therefore, when a transmission erroroccurs, resulting in necessity of resending data, the 16 QAM, the QPSKand the BPSK will be chosen for the modulation method step by step toachieve more secure transmission. Likewise, for the coding rate, since ½offers stronger error resistance characteristic than ¾, if atransmission error occurs, use of ½ will enable enhanced errorresistance characteristic.

Further, also the MIMO signal processing method can transmit dataefficiently in the similar manner by using the above-stated STBC whenthere are many transmission errors, and by using the SDM when conditionsof the transmission matrix are good, that is, a distance betweentransceivers is short, for example, resulting in less data errors.

Conventionally, when facing deteriorated transmit conditions, a physicallayer that controls coding, the MIMO signal processing andmodulation/demodulation cannot receive the NACK frame and the ACK/NACKframe itself. Accordingly, its parameters are changed to reduce the datarate for example, and thus, the data transmission is tried. Therefore,the same operations are performed without discriminating data thatrequires latency like an audio signal or video streaming from otherdata, for example, thus offering a problem of inefficiency.

While describing a wireless transceiver that executes communicationbased on priority of data, the above-stated patent references 1 and 2 donot disclose the priority of data that is applied to an MIMO wirelesstransceiver by way of example. In addition, the above-stated patentreference 3 discloses a configuration in which a wireless communicationsystem capable of MIMO transmission and reception switches pathsaccording to degree of importance of data as shown by a tag of a datasegment, but only switching is made between the MIMO transmission andreception modes that use a plurality of antennas and the mode that usesonly one antenna. Thus, the wireless communication system does not offerconsideration on SDM and the STBC, which are transmission systems usedfor the above-stated MIMO wireless transceiver.

The present invention has been made to solve the above-describedproblems. It is an object of the present invention to provide a wirelesscommunication system comprising a MIMO wireless transceiver, in whichcoding, MIMO signal processing and a modulation method are controlledaccording to priority of transmission data. More specifically, theobject of the invention is to provide a wireless communication systemcapable of securely transmitting data with higher priority, therebyimproving the total throughput when a plurality of types of data aretransmitted.

To solve the above-stated problems, in a wireless transceiver thatexecutes MIMO transmission according to the present invention, prioritycontrol that judges priority of transmit data and a transmission modetable are provided to control an option as to which MIMO transmissionsystem SDM or STBC is selected to transmit, a coding rate and modulationmethod based on priority of transmission data and a transmission mode ofa transmission destination when the data is transmitted.

As a general rule, when priority is sufficiently high and errors shouldbe reduced as much as possible, the STBC is used as a transmissionmethod, the modulation method is set to BPSK, and the coding rate is setto be higher. When priority is lower, the setting should be reversed,wherein SDM is used as a transmission method, the modulation method isset to 64QAM and the coding rate is set to be lower. The status ofcommunication matrix can be judged by the presence or absence ofreception of an ACK frame or a NACK frame that is exchanged betweentransceivers, signal strength, and an eigen value of a transfer matrixas well.

As stated above, according to the wireless transceiver according to thepresent invention, it becomes possible to choose a MIMO signalprocessing method more flexibly, thus enabling further efficientwireless transmission of data having higher priority.

As stated above, since the MIMO wireless transceiver according to thepresent invention is arranged to choose coding, MIMO signal processingand modulation methods according to priority of transmit data, it ispossible, in particular, to reduce the number of retransmission, shortenof transmission delay time and improve throughput, which are related totransmission of transmit data having higher priority, as compared with aconventional system wherein coding, MIMO signal processing andmodulation methods are chosen according only to the status oftransmission matrix regardless of priority of data. In addition, moreflexible data transmission becomes possible, and further reduction inthe number of retransmission times, shortening of transmission delaytime and improvement in throughput can be achieved by using transmissionmatrix information that is obtained by applying the following twomethods and coding, MIMO signal processing and modulation methods thatare determined based on a transmission mode table according to priorityof transmit data. One of the two methods is to learn the status oftransmission matrix based on the reception power strength of aresponding frame for transmit data or on an eigen value of transmissionmatrix that is obtained in MIMO signal processing. The other is to learnthe status of transmission matrix by transmitting data after addition ofinformation on the transmission matrix to a responding frame when areceiver receives transmission data, and allowing the transmitter toobtain this information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a transceiver according to a firstembodiment of the present invention;

FIG. 2 is a block diagram of a wireless transceiver of a wireless LANsystem according to a prior art;

FIG. 3 is a diagram illustrating transmission data being stored in apriority control queue in a priority control of transmit data;

FIG. 4 is a diagram illustrating a transmission mode table by way ofexample;

FIG. 5 is a graph showing a rule for determining coding, MIMO signalprocessing and a modulation method;

FIG. 6 is a flow chart illustrating the outline of transmission andreception according to the first embodiment of the present invention;

FIG. 7 is a flow chart illustrating detailed transmission operationsaccording to the first embodiment of the present invention;

FIG. 8 is a flow chart illustrating detailed operations in a receptionstep according to the first embodiment of the present invention;

FIG. 9 is a flow chart illustrating detailed steps for receiving aresponding frame according to the first embodiment of the presentinvention;

FIG. 10 is a configuration diagram of a transceiver according to asecond embodiment of the present invention;

FIG. 11 is a configuration diagram for measurement of reception signalstrength at a reception RF unit; and

FIG. 12 is a configuration diagram of a transceiver according to a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will be described belowwith reference to FIGS. 1 and 4 to 12.

First Embodiment

A first embodiment according to the present invention will be describedhereinafter with reference to FIGS. 1 and 4 to 9.

First, a configuration of a transceiver according to the embodiment ofthe present invention will be described with reference to FIG. 1.

FIG. 1 is a block diagram of a transceiver 2 according to the firstembodiment of the present invention.

In the MIMO wireless receiver according to the first embodiment of thepresent invention, transmit data 3 a is buffered in a priority controlunit 10 a and is controlled so that data having higher priority can bepreferentially transmitted ahead of others.

A MIMO wireless communication system 1 shown in the embodiment is suchthat a wireless transceiver 2 a and a wireless transceiver 2 b performdata communication wirelessly through a plurality of antennas.

The wireless transceiver 2 a on the transmission side includes apriority control unit 10 a, an encoder 11 a, a MIMO signal processingunit 12 a, a modulator 13 a, a transmission RF unit 14 a, a transmissionmode table processing unit 15 a, and a coding/MIMO modulation controlunit 16 a.

The transmit data 3 a is input to the priority control unit 10 a and isbuffered in accordance with priority of data as described earlier forthe background art. Then, the transmit data is encoded by the encoder 11a for correcting errors and is input to the MIMO signal processing unit12 a.

The MIMO signal processing unit 12 a, as described earlier for thebackground art, generates two transmission streams using either one ofthe SDM or the STBC transmission system. Thereafter, the transmissionstreams are modulated by using an appropriate modulation method in themodulator 13 a, and are up-converted into radio-frequency signals in thetransmission RF unit 14 a. Then the signals are passed through atransmission/reception selector switch 17 a and are transmitted from anantenna 18 a.

Operational description up to this process is the same as that for thebackground art. Here, the priority control unit 10 a has a function inwhich, when data controlled by the priority control unit 10 a istransmitted, information indicating which transmit data is classifiedinto which priority, and an MAC address which is a physical identifiershowing a transmission destination are transmitted to the transmissionmode table processing unit 15.

The transmission mode table processing unit 15 searches a transmissionmode table for a transmission mode on the basis of the MAC address ofthe transmission destination. The transmission mode table-processingunit 15 includes MAC addresses and transmission modes associated witheach other, which will be described later.

Subsequently, the coding/MIMO/modulation control unit 16 a determinescoding, MIMO signal processing and modulation methods of respectivetransmit data, based on the transmission mode retrieved by thetransmission mode table processing unit 15 and priority of transmit datathereof, and delivers the coding, MIMO signal processing and modulationmethods to the above-stated encoder 11 a, the MIMO signal processingunit 12 a and the modulator 13 a, respectively.

The transmission data is subjected to encoding, MIMO signal processingand modulation in respective units based on the information delivered,and is up-converted to a radio-frequency signal in the transmission RFunit 14 a, and the signal is then transmitted from the antenna 18 a.

The wireless receiver 2 b on the receiver side transmits a respondingframe in the same steps as those stated for the background art.

The wireless transmitter 2 a processes the responding frame received inthe same way as that described earlier for the background art forretransmission control.

Next, an example of a structure of the transmission mode table as wellas a rule to determine the MIMO system, the coding and the modulationmethod will be described with respective to the transmission mode withreference to FIGS. 4 and 5.

FIG. 4 is a diagram illustrating an example of a transmission modetable. FIG. 5 is a graph showing a rule to determine coding, MIMO signalprocessing and a modulation method.

A transmission mode table 164 stores an identifier which uniquelyidentifies a communication destination, a transmission mode whichindicates status of transmission matrix and time when a signal isreceived from the communication destination. Here, an MAC address isused for the identifier which uniquely identifies a communicationdestination. The status of transmission matrix should be stored for eachcommunication destination since the status differs from destination todestination. Here, four levels M1 to M4 are arranged for thetransmission matrix status. It shall be specified that the level M1means the best status of communication matrix, and the level M4 meansthe worst status thereof. Status of transmission matrix may be specifiedmore meticulously. In addition, since status of transmission matrixchanges from time to time, effectiveness of information on thetransmission matrix can be known by storing the status along with timeinformation.

Then, based on priority of transmit data and transmission mode requestedand by applying a certain rule as well as coding, MIMO signal processingand modulation methods are determined.

It should be noted that priority of transmission data shall have beenclassified into four priority levels as described earlier for thebackground art. On the other hand, the transmission mode indicatingstatus of transmission matrix is either one of four levels M1 to M4.

MIMO signal processing can be determined, for example, according to agraph 151 in FIG. 5.

For example, when priority is AC_VD (maximum), a first MIMO signalprocessing method is used if transmission mode is in the level M1(transmission matrix: good), and a second MIMO signal processing methodis used if transmission mode is either one of the levels M2 to M4 (161).When priority is AC_VO, the second MIMO signal processing method is usedregardless of the transmission mode. Likewise, selection of codingmethod and modulation method (graphs 162 and 163 in FIG. 5) can beuniquely determined based on priority and transmission mode. Thefollowing table 2 shows correspondence between such priority levels and,MIMO signal processing, coding and modulation methods.

TABLE 2 Transmit priority mode AC_BG AC_BE AC_VD AC_VO MIMO M1 SDB SDMSDM STBC method M2 SDM SDM STBC STBC M3 SDM STBC STBC STBC M4 STBC STBCSTBC STBC Coding M1 ¾ ¾ ¾ ½ M2 ¾ ¾ ½ ½ M3 ¾ ½ ½ ½ M4 ½ ½ ½ ½ ModulationM1 64QAM 64QAM 64QAM QPSK M2 16QAM 16QAM QPSK BPSK M3 QPSK QPSK BPSKBPSK M4 BPSK BPSK BPSK BPSK

Next, operations of the wireless transceiver according to the firstembodiment of the present invention will be described with reference toFIGS. 6 to 9.

First, operation steps showing the outline of transmission and receptionwill be described with reference to FIG. 6.

FIG. 6 is a flow chart illustrating the outline of transmission andreception according to the first embodiment of the present invention.

The wireless receiver, upon initiating operations (S0), continuouslychecks the presence or absence of a receiving signal (S1) as well asthat of transmit data (S2). When a receiving signal is present, thewireless receiver executes reception processing (S10) and, again, shiftsthe step to an operation to confirm the presence or absence of anyreceiving signal (S1). When transmission data is present, the wirelessreceiver executes transmission processing (S20), and shifts the step toreceive a responding frame (S11) after completion of transmission.

Next, detailed steps of transmission processing (S20) will be describedwith reference to FIG. 7.

FIG. 7 is a flow chart illustrating detailed transmission operationsaccording to the first embodiment of the present invention.

When transmission processing (S20) is initiated (S200), the wirelesstransceiver receives priority of transmit data and an MAC address fromthe priority control unit 10 (S201). Based on these values, thetransmission mode table processing unit 15 selects a transmission mode,as stated earlier, which is associated with the MAC address of thetransmission destination, in accordance with a value on the transmissionmode table (S202). Based on the value of transmission mode obtained inthe above-stated step, the coding/MIMO signal processing/modulationcontrol unit 16, as already described in the above-stated example,determines the coding rate, the MIMO signal processing method and themodulation method. Based on the information, the encoder 11, the MIMOsignal processing unit 12 and the modulator 13 execute their ownprocessing (S203), and finally, the data is transmitted from the antenna18 (S204).

Next, detailed steps of reception processing (S10) will be describedwith reference to FIG. 8.

FIG. 8 is a flow chart illustrating detailed operations in receptionstep according to the first embodiment of the present invention.

When reception processing (S10) is initiated (S100), the wirelesstransceiver first judges whether or not the data is addressed to the ownstation (S101). When the data is not addressed to the own station, thewireless transceiver terminates the reception processing (S105). Whenthe data is addressed to the own station, the wireless transceiverchecks the presence or absence of any reception frame errors (S102). Ifthere is no error in the reception frame, the transceiver transmits anACK frame that notifies successful reception (S103) and terminates thereception processing (S105). If any errors exist in the reception frame,the transceiver transmits a NACK frame that notifies unsuccessfulreception (S104) and terminates the reception processing (S105).

Next, detailed steps for receiving a responding frame (S11) will bedescribed with reference to FIG. 9.

FIG. 9 is a flow chart illustrating detailed steps for receiving aresponding frame according to the first embodiment of the presentinvention.

When reception of a responding frame (S11) is initiated (S110), thewireless transceiver is put in the status of waiting for reception of aresponding frame (S111). When an ACK frame is received within aspecified time period or in prescribed timing (S112), the status oftransmission matrix is judged to be good, and the transmission modelevel is incremented by 1 (S115). For example, when the transmissionmode is M2, the mode will be set to M1. When a NACK frame is receivedwithin a specified time period or in prescribed timing (S113), thestatus of transmission matrix is judged to be poor, and the transmissionmode value is decremented by 1 (S116). For example, when thetransmission mode is M2, the mode will be set to M3. When a respondingframe is not received within a specified time period or in prescribedtiming (S114), the status of transmission matrix is judged to be verypoor, and the transmission mode value is decremented by 2 (S117). Forexample, when the transmission mode is M2, the mode is set to M4.

The operations shown above makes it possible to realize a wirelesstransceiver constituting a wireless communication system that controlscoding, MIMO signal processing and modulation methods according topriority of transmit data.

With the embodiment, a transmission mode value of the transmissioncontrol table is changed depending on the presence or absence ofreception of a responding frame, and coding, MIMO signal processing andmodulation methods are determined based on the changed transmission modevalue and priority. However, when transmit data having the highestpriority is transmitted, it may be preliminary determined to have afixed arrangement that enables selection of coding rate, MIMO signalprocessing and modulation methods that enables most assured transmissionof data even at the sacrifice of data rate.

Second Embodiment

Hereinafter, a second embodiment according to the present invention willbe described with reference to FIGS. 10 and 11.

FIG. 10 is a block diagram of a transceiver according to the secondembodiment of the present invention.

FIG. 11 is a configuration diagram for measurement of reception signalstrength at a reception RF unit.

With the first embodiment, quality of a transmission matrix is assumedby using a responding frame, and the transmission mode table is updatedbased on the quality assumption.

On the other hand, the second embodiment refers to a method whereinquality of a transmission matrix is assumed based on reception signalstrength upon receipt of a responding frame and the transmission tableis updated based on the quality assumption.

As shown in FIG. 10, with the embodiment, it is possible to learnquality of a transmission matrix by measuring strength of a receptionsignal in a reception RF unit 20 and notifying the signal strength ofthe transmission mode table. This is because it can be judged thatquality of a transmission matrix becomes better as the reception signalstrength becomes larger.

A specific method for measuring the reception signal strength in thereception RF unit is as shown in FIG. 11. That is to say, a signalreceived from the antenna 18 is amplified with a low-noise amplifier 201and part of the amplified signal is input to a reception power strengthdetector 203 by using a directional coupler 202.

Third Embodiment

Hereinafter, a third embodiment according to the present invention willbe described with reference to FIG. 12.

FIG. 12 is a configuration diagram of a transceiver according to thethird embodiment of the present invention.

In this embodiment, data from a reception MIMO signal processing unit isused for assuming quality of a transmission matrix and updating atransmission mode table based on the assumed quality.

In the reception MIMO signal processing unit, a transmission matrix isset up for receiving a MIMO signal. Therefore, it is possible to assumequality of the transmission matrix by obtaining eigen values of thetransmission matrix upon receipt of a responding frame and judging sizesof such eigen values. Judgment is made that the status of transmissionmatrix is better as the total of eigen values is larger, or conversely,the status of transmission matrix is poorer as the total of eigen valuesis smaller. Base on such judgment, it is possible to update thetransmission table 15.

The above-stated embodiments can provide a wireless communication systemcomposed of a MIMO wireless transceiver, in which coding, MIMO signalprocessing and modulation methods are controlled according to priorityof transmission data. More specifically, a wireless communication systemcan be provided which executes assured transmission of data havinghigher priority and improves throughput in total when a plurality oftypes of data are transmitted.

As described above, the present invention can provide a wirelesscommunication system composed of an MIMO wireless transceiver, in whichcoding, MIMO signal processing and modulation methods are controlledaccording to priority of transmit data.

1. A wireless transceiver which executes transmission and reception ofdata wirelessly by using at least two antennas, said wirelesstransceiver comprising: a priority control unit which judges priority oftransmit data, said priority being predetermined; and a transmissionmode table in which an identifier that uniquely identifies atransmission destination is associated with a transmission mode thatindicates channel status of transmission matrix of a communicationdestination for each said transmission destination, wherein a switchingis made between a Space Division Multiplexing (SDM) method and a SpaceTime Coding (STC) method, based on priority of said transmit data,wherein said SDM method distributes as a plurality of transmissionstreams, and transmits said transmit data, wherein said STC methodperforms time-space encoding on said transmit data, and wherein, whendata is transmitted to a transmission destination identified by saididentifier, a switching is made between said SDM method and said STCmethod based on the priority of said transmit data and the transmissionmode of said transmission mode table.
 2. The wireless transceiveraccording to claim 1, further comprising: wherein said transmission modeis updated to another transmission mode that is associated with saidtransmission destination based on a reception signal from saidtransmission destination.
 3. The wireless transceiver according to claim2, wherein, if reception data is received without error upon receipt ofthe data, an ACK frame is transmitted within a specified time period orin prescribed timing, and if the reception data is received erroneously,a NACK frame is transmitted within a specified time period or inprescribed timing, and wherein said transmission mode is updated basedon the presence or absence of reception of the ACK frame or the NACKframe.
 4. The wireless transceiver according to claim 2, wherein, ifreception data is received without error upon receipt of the data, anACK frame is transmitted within a specified time period or in prescribedtiming, and if the reception data is received erroneously, a NACK frameis transmitted within a specified time period or in prescribed timing,and wherein said transmission mode is updated based on signal strengthof a reception signal of the ACK frame or the NACK frame.
 5. Thewireless transceiver according to claim 2, wherein if reception data isreceived without error upon receipt of the data, an ACK frame istransmitted within a specified time period or in prescribed timing, andif the reception data is received erroneously, a NACK frame istransmitted within a specified time period or in prescribed timing, andwherein said transmission table is updated based on an eigen value of atransmission matrix of a reception signal of the ACK frame or the NACKframe.
 6. The wireless transceiver according to claim 2, wherein ifreception data is received without error upon receipt of the data, anACK frame is transmitted within a specified time period or in prescribedtiming, and if the reception data is received erroneously, a NACK frameis transmitted within a specified time period or in prescribed timing,and wherein said transmission table is updated based on a channelinformation of the ACK frame or the NACK frame.
 7. The wirelesstransceiver according to claim 2, wherein if reception data is receivedwithout error upon receipt of the data, an ACK frame is transmittedwithin a specified time period or in prescribed timing, and if thereception data is received erroneously, a NACK frame is transmittedwithin a specified time period or in prescribed timing, and wherein saidtransmission table is updated based on a channel information of the ACKframe or the NACK frame.
 8. A wireless transceiver which executestransmission and reception of data wirelessly by using at least twoantennas, said wireless transceiver comprising: a priority control unitwhich judges priority of transmit data, said priority beingpredetermined; and wherein a switching is made between a Space DivisionMultiplexing (SDM) method and a Space Time Coding (STC) method, based onpriority of said transmit data, wherein said SDM method distributes as aplurality of transmission streams, and transmits said transmit data,wherein said STC method performs time-space encoding on said transmitdata, and wherein either a modulation method or a coding method isselected based on the priority that is judged in said priority controlunit.
 9. The wireless transceiver according to claim 8, wherein saidtransmission mode is updated to another transmission mode that isassociated with said transmission destination based on a receptionsignal from said transmission destination.
 10. The wireless transceiveraccording to claim 9, wherein, if reception data is received withouterror upon receipt of the data, and ACK frame is transmitted within aspecified time period or in prescribed timing, and if the reception datais received erroneously, a NACK frame is transmitted within a specifiedtime period or in prescribed timing, and wherein said transmission modeis updated based on a channel information of the ACK frame or the NACKframe.
 11. The wireless transceiver according to claim 9, wherein ifreception data is received without error upon receipt of the data, anACK frame is transmitted within a specified time period or in prescribedtiming, and if the reception data is received erroneously, a NACK frameis transmitted within a specified time period or in prescribed timing,and wherein said transmission table is updated based on a channelinformation of the ACK frame or the NACK frame.
 12. A wirelesstransceiver which executes transmission and reception of data wirelesslyby using at least two antennas, said wireless transceiver comprising: apriority control unit which judges priority of transmit data, saidpriority being predetermined; and wherein a switching is made between aSpace Division Multiplexing (SDM) method and a Space Time Coding (STC)method, based on priority of said transmit data, wherein said SDM methoddistributes as a plurality of transmission streams, and transmits saidtransmit data, wherein said STC method performs time-space encoding onsaid transmit data, and wherein, when said priority is low, said SDMmethod is used, and when said priority is high, said STC method is used.13. The wireless transceiver according to claim 12, wherein saidtransmission mode is updated to another transmission mode that isassociated with said transmission destination based on a receptionsignal from said transmission destination.
 14. The wireless transceiveraccording to claim 13, wherein, if reception data is received withouterror upon receipt of the data, and ACK frame is transmitted within aspecified time period or in prescribed timing, and if the reception datais received erroneously, a NACK frame is transmitted within a specifiedtime period or in prescribed timing, and wherein said transmission modeis updated based on a channel information of the ACK frame or the NACKframe.
 15. The wireless transceiver according to claim 13, whereinreception data is received without error upon receipt of the data, anACK frame is transmitted within a specified time period or in prescribedtiming, and if the reception data is received erroneously, a NACK frameis transmitted within a specified time period or in prescribed timing,and wherein said transmission table is updated based on a channelinformation of the ACK frame or the NACK frame.